Generally, a rotary body to be rotated at high speeds, such as a crankshaft of an engine, is required to be accurately balanced about an axis thereof, in order to suppress vibration during rotation, etc. In this situation, if positional accuracy of center holes for use during machining the rotary body is poor, a rotational imbalance amount in the rotary body becomes larger. Therefore, it is necessary to adequately set positions of the center holes.
As a technique for setting the center-hole positions, the following Patent Document 1 discloses the following method. In the method disclosed in the Patent Document 1, first of all, a three-dimensional shape of a forged rotary body in a blank (pre-machining) state. Based on the resulting measurement values, temporary center holes are set up. Through simulation of machining on the basis of the temporary center holes, a virtual shape of the rotary body in a post-machining state is calculated. A rotational imbalance amount in the virtual shape is calculated. Then, when the calculated rotational imbalance amount falls within a correctable range, the temporary center holes are set as center holes for use during actual machining.